Interconnection Technologies

1. Interconnection Technologies • Routing I

2. Will layer 2 networking suffice?

3. Layer 3 usually provides • Internetworking for data link technologies • Globally unique addresses • Scalable routing • A common communications format • Packet fragmentation capability • A hardware independent interface • Packet independence

4. Routers • Typically a special purpose, dedicated device • Connects heterogenous networks • Directs packets towards ultimate destination • Dynamic routing algorithsm often used • Make automatic forwarding decisions • Can forward based on various metrics • Also called a gateway • Offical pronounciation is really rooter

5. Routing • Scope • Autonomous system, interior, exterior • Dynamic routing • Protocol for route exchange and computation • Static routing • Manually configured routes • Destination address driven

6. Internet protocol (IP) • Standardized in RFC 791 • Connectionless • Unreliable • Fairly simple • The Internet Glue

7. IP addresses • Virtual – not bound to hardware • 32-bit fixed size • Unique address for each IP interface • Global authories assign a prefix (network) • Local administrators assign the suffix (host) • Usually written as dotted decimal notation • e.g. 140.192.1.6

8. Classful IP addressing

9. IP address notation

10. Classful address sizes

11. Limitations of classful addressing • Internet growth • Route table size • Address depletion • Misappropriation of addresses • Lack of support for different sized networks • Class B too big, class C too small

12. IP addressing solutions • Subnetting • Supernetting • Classless interdomain routing (CIDR) • Variable length subnet masks (VLSM)

13. Subnetting

14. Subnet mask • The bit length of the prefix (network) • Prefix (network) is no longer classful • Dotted decimal or '/' notation • 140.192.1.6's subnet mask is 255.255.255.128 • ...or 140.192.1.6/25 • You may want to convert to binary for clarify • A /25 or 255.255.255.128 subnet mask is: • 11111111.11111111.11111111.10000000

15. Supernetting • Combine smaller blocks into larger aggregate • If class B too big, class C too small... • Maybe do this: • Combine 199.63.0.0/24 to 199.63.15.0/24 • Equals 199.63.0.0/20

16. CIDR • Use supernetting for routing tables • Routes advertised as smaller CIDR blocks • So instead of advertising: • 199.5.6.0/24, 199.5.6.1/24, 199.5.6.2/24 and 199.5.6.1/24 separately • Advertise: • 199.5.6.0/22 one time • Internet CIDR report • http://www.employees.org/~tbates/cidr-report.html

17. VLSM • Multiple subnet sizes in a single AS • Allows efficient use of address space • Can be used to build internal hierarchy • External view of AS does not change • An organization may have 140.192.0.0/16 • But internally may use 140.192.0.0/17, 140.192.128.0/24, 140.192.129.0/24 and so on.

18. Special IP addresses

19. Obtaining IP addresses • IANA has global authority for assignment • Regional registries delegate (ARIN/RIPE/APNIC) • ISPs assign addresses to end end users • RFC 1918 defines private address netblocks • NOT globally unique • Must not appear on the public Internet • 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16

20. IP networking example

21. IP router addressing example

22. IP datagram layout

23. Final thoughts • IP is unreliable • IP addressing can be a pain • IPv6 doesn't make it any easier • IP address is both a who and a where • IP addresses provide little security • Private IPs and NAT are best avoided